Chem Chapter 17

Positron emission

(0/+1)

Electron

(0/-1) e

Beta rays

(0/-1)e

Gamma rays

(0/0)y

Neutron

(0/1) N

Proton symbol

(1/1) P

Alpha rays

(4/2)a

Carbon - 14

- is all around us in the environment C-14 is constantly formed in upper atmosphere of earth - C-14 then decays by beta emission; half-life = 5730 years - ( _6_14_C→_7_14_N_ + _−1_0_e__) - Losing beta particle - Constant production and decay of C-14 creates equilibrium concentration in atmosphere

Curie

= 3.7 x 1010 decay events per second

Gamma particle

A gamma ray has no charge and no mass. Gamma rays are usually emitted in conjunction with other types of radiation. The alpha emission of U-238 is accompanied by the emission of a gamma ray.

Alpha radiation

Alpha (α) Radiation occurs when an unstable nucleus emits an α particle composed of 2 protons and 2 neutrons.

Penetrating power of alpha particles

Because of its large size, alpha radiation has the —--- the ability to penetrate matter. Alpha radiation does not easily penetrate cells; it can be stopped by a sheet of paper, by clothing, or even by air. A low-level alpha emitter kept outside the body is relatively safe. If an alpha emitter is ingested or inhaled, it becomes very dangerous because the alpha particles then have direct access to the biological molecules that compose organs and tissues.

Radio carbon dating

C-14 get into plants via photosynthesis and get into all living organisms When something dies it stops taking in new C-14; only decay of C-14 Amount of C-14 in an artifact indicates its age Carbon dating can be checked against objects of known ages - accurate method Not dependable for dating more than 50,000 yrs old (C-14 too low to measure)

Gamma radiation

Different from alpha or beta radiation - Gamma radiation is not matter, but electromagnetic radiation. Gamma rays are high-energy (short-wavelength) photons. The symbol for a gamma ray is as follows:

Curie Nobel Prize in Chemistry

Element 96 (curium) is named in honor of Marie Curie and her contributions to our understanding of radioactivity. Marie Curie with her two daughters. Irene (right) became a distinguished nuclear physicist in her own right, winning a Nobel Prize in 1935. Eve (left) wrote a highly acclaimed biography of her mother.

Geiger-Muller counter

Energetic particles emitted by radioactive nuclei pass through a chamber filled with argon gas and ionize it. When an argon atom is ionized, it is attracted to the anode and the dislodged electron is attracted to the cathode, creating a tiny electrical current. This electrical signal can be detected on a meter or turned into an audible click. The faster the clicks, the more radiation is being emitted.

Antoine-Henri Becquerel

In 1896, French scientist Antoine-Henri Becquerel (1852-1908), discovered radioactivity. Becquerel hypothesized that invisible emission of X-rays was associated with the visible greenish glow of phosphorescence. To test his hypothesis, he placed crystals of potassium uranyl sulfate on top of a photographic plate wrapped in black cloth. He placed the wrapped plate and the crystals outside to expose them to sunlight to make them phosphoresce. If the crystals emitted X-rays as they phosphoresced, the X-rays would pass through the black cloth and expose the underlying photographic plate. The photographic plate did show a bright exposure spot where the crystals had been.

Curie Nobel Prize in Physics

In 1903, Curie received the Nobel Prize in physics—which she shared with Becquerel and her husband, Pierre Curie—for the discovery of radioactivity. In 1911, Curie was awarded a second Nobel Prize, this time in chemistry, for her discovery of the two new elements polonium and radium.

Scintillating counter

In a scintillation counter, the radioactive emissions pass through a material (such as NaI or CsI) that emits ultraviolet or visible light in response to excitation by energetic particles. This light is detected and turned into an electrical signal that can be read on a meter.

The Discovery of Radioactivity: Marie Curie

Marie Curie (1867-1934) pursued the study of uranic rays for her doctoral thesis. Her first task was to determine whether any other substances besides uranium emitted uranic rays. Curie discovered two new elements, both of which also emitted uranic rays. Curie named one of her newly discovered elements polonium after her home country of Poland.

Natural Radioactivity

Naturally occurring radioactive elements in our environment are all undergoing radioactive decay. The ground beneath you and the food you eat contain a residual number of radioactive atoms that enter into your body fluids and tissues. Small amounts of radiation from space make it through our atmosphere and constantly bombard Earth. Humans and other living organisms have adapted to survive in it. Scientists have to take background readings before experiments to make sure they aren't measuring radioactivity coming from the table or floor.

Other uses of fission

Nuclear power - energy released slowly over time Fission heat boil water steam turns a turbine on a generator Fission occurs in the nuclear core or reactor U-235 fuel rods interspersed with neutron absorbing control rods

Positron penetration

Positron emission is similar to beta emission in its ionizing and penetrating power.

Positron

Positron emission occurs when an unstable nucleus emits a positron. As the emission occurs, a proton turns into a neutron. opposite of beta emission

Environmental radon

Radon—a radioactive gas—is one of the products of the natural radioactive decay series of uranium. Wherever there is uranium in the ground, there is likely to be radon seeping up into the air. If the gas is trapped in a dwelling enclosure, radon and its daughter nuclides can attach to dust particles and then be inhaled into the lungs, where they decay radioactively and increase lung cancer risk. The radioactive decay of radon is by far the single greatest source of human radiation exposure. Radon-222 has a half-life of 3.8 days.

ionizing power

The ability of radiation to ionize molecules and atoms is called its If radiation ionizes molecules within the cells of living organisms, those molecules become damaged and the cell can die or begin to reproduce abnormally.

Fission chain reaction

The neutrons produced by the fission of one uranium nucleus induce fission in other uranium nuclei to produce a chain reaction.

Nuclear equations

The term nuclide is used in nuclear chemistry to mean a specific isotope. The original atom is called the parent nuclide, and the products are called the daughter nuclides. When an element emits an alpha particle, the number of protons in its nucleus changes, transforming it into a different element. In chemical reactions, elements retain their identity; in a nuclear reaction, elements often change their identity as a result of a change in the number of protons in the nucleus.

Types of radiation

There are several different types of radioactive emissions: alpha (α) particles, beta (β) particles, gamma (γ) rays, and positrons. Nuclei are unstable when they are too large or contain an unbalanced ratio of neutrons to protons. Small nuclei need about 1 neutron to every proton to be stable, while larger nuclei need about 1.5 neutrons to every proton.

Gamma penetration

They have the lowest ionizing power but the highest penetrating power. (Imagine a motorbike zipping through a traffic jam.)

Half Life

Time it takes for half of the parent nuclides to decay into daughter nuclides

Nuclear fusion

Two lighter nuclei combine to form heavier one Emits large amounts of energy Occurs in stars (like the sun) and basis of hydrogen bomb High temperatures are required because two positively charge nuclei repel

Beta particles

a negatively charged particle (an electron) emitted from the nucleus of an atom during radioactive decay.

Roentgen

amount of radiation that produces 1 coulomb of charge in 1 cm3 of dry air at STP

Film Badge Dosimeter

consist of photographic film held in a small case that is pinned to clothing. The badges are collected and processed as a way to monitor exposure to radiation. The more exposed the film has become in a given period of time, the more radioactivity to which the person has been exposed.

Genetic defects

damage to DNA of reproductive cells; only seen in animals so far

Ernest Rutherford

focused on characterizing the radioactivity itself. These scientists found that the emissions were produced by the nuclei of radioactive atoms. The radioactive nuclei were unstable and would emit small pieces of themselves to gain stability. These were the particles that Becquerel and Curie detected.

gamma rays

high-energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground energy state

Radiation

is the emission of tiny energetic particles by the nuclei of certain unstable atoms.

Acute radiation damage

large exposure over short period of time (nuclear bombs, nuclear reactor cores); kills cells and weakens immune system

Becquerel's experiment

later retracted his results when he discovered that a photographic plate with potassium uranyl sulfate crystals showed a bright exposure spot even when the plate and the crystals were stored in a dark drawer and were not exposed to sunlight nor emitting phosphorescence. Becquerel realized that the crystals were constantly emitting something that exposed the photographic plate. Becquerel concluded that it was the uranium within the crystals that was the source of the emissions, and he called the emissions uranic rays.

Beta particle

lower ionization energy greater penetrating power than alpha greater risk to body outside less dangerous inside body than alpha

Beta radiation

occurs when an unstable nucleus emits an electron. As the emission occurs, a neutron turns into a proton.

positrons

positively charged electrons

alpha particles

positively charged particles with about four times the mass of a hydrogen atom

Radiation and ions

radiation causes ions

Cancer

radiation damages DNA; can cause cells to grow abnormally and start dividing and growing uncontrollably

Radiotherapy

radiation is effective at killing rapidly dividing cells, so it can be used to treat cancer

Isotope scanning

radioactive isotope given to patient; different isotopes taken up by different organs or tissues; can be used to detect cancer, thyroid problems, or image organs

Penetrating power

the ability to penetrate matter. In order for radiation to damage important molecules within living cells, it must penetrate the cell.

Nuclear Fission

the splitting of the atom An atom of uranium is bombarded with a neutron Splits the U into two lighter elements Process produces 3 neutrons Nuclear fission emits enormous amounts of energy

Radiation sickness

vomiting, skin burns, hair loss